The present invention relates to a joint for interconnecting a web and a chord in a structural member and, more particularly, to an improved high strength, modified dovetail joint for joining a plywood web to a wooden chord.
Many joint constructions are known in the art for joining wooden webs to wooden chords. Of these several are modified dovetail type joints for interconnecting a plywood web to a solid wood chord. One specific joint construction is disclosed in U.S. Pat. No. 3,991,535, issued Nov. 16, 1976 to Keller et al. The Keller et al. joint is characterized as a pressed-in dovetail type joint. The Keller et al. joint includes two relatively inclined grooves in the chord that intersect each other at a location above the surface of the chord. Flexible tongues are formed on the edge portion of the plywood web and are constructed and sized to be received in respective ones of the grooves in the plywood chord. The Keller et al. construction requires that the lower terminus of the glue lamina or joint between each of the plurality of layers of veneer in the plywood web be located above the surface of the chord. Although a joint of the Keller et al. type is suitable for many structural purposes, it has been found that when a finished structural member employing a joint of the Keller et al. type is placed under loading, the adhesive bond between the layers of veneer forming the tongues and the adjacent intervening layer of veneer will tend to separate, weakening the joint. The separation of the adhesive bond, that is the failure of the adhesive laminae between the layers of veneer, is due at least in part to the interrelationship of the chord grooves and the bendable tongues on the web. For example, when a structural member employing a Keller et al. type joint is placed under a load, the glue laminae between the layers of veneer in the web are placed under a strain loading, which the ordinary glue laminae in plywood is not intended to withstand, causing the glue joint and resultant delamination or separation of the layers of veneer in the plywood web adjacent the chord. When this occurs, a substantial portion of the strength of the joint is lost and can, under certain circumstances, lead to complete failure of the joint between the web and the chord.
It is a broad object of the present invention to provide a modified dovetail joint that corrects the foregoing problem inherent in the type of modified dovetail joint just discussed and other joints of similar construction for joining a plywood web to a chord composed of solid wood or other material. It is another object of the present invention to provide a joint for interconnecting a plywood web and a chord that is self-locking once the web and chord are joined, thus eliminating the need for clamping the two while awaiting the cure of adhesive normally used to permanently bond the web to the chord. It is a further object of the present invention to provide an improved and modified dovetail joint that requires a minimum of adhesive for permanently affixing the web to the chord and still a further object of the present invention to provide a modified dovetail joint in which flexible tongues on a plywood web are inserted into respective inclined grooves in a chord that requires a minimum of material to be removed from the plywood web in order to construct the flexible tongues and at the same time produces joint structure having higher strength than those of the prior art.